The lead-free perovskite BiFeO3 has received considerable attention for non-volatile memory applications because of its large polarization of ˜100 μC/cm2 along the [111] direction. See Wang et al., Science 299, 1719 (2003); Li et al., Appl. Phys. Lett., 84, 5261 (2004); Das et al., Appl. Phys. Lett., 88, 242904 (2006); Legeugle et al., Appl. Phys. Lett., 91, 022907 (2007). Epitaxial growth of BiFeO3 on silicon has been demonstrated using an intervening epitaxial SrTiO3 buffer layer. See Wang et al., Appl. Phys. Lett., 85, 2574 (2004). However, these as-grown BiFeO3 films exhibit relatively high coercive field (Ec), high leakage current, and reduced reliability, rendering the films less than desirable candidates for integrated microelectronic devices. See Ramesh et al., Nat. Mater., 6, 21 (2007). Furthermore, such films may be strained, a characteristic which may lead to degraded film properties and other unwanted effects.
In addition to its large ferroelectric polarization, BiFeO3 is a multiferroic material with a high ferroelectric Curie temperature (˜820° C.)7 and a high antiferromagnetic Néel temperature (˜370° C.). See G. Smolenskii, V. Isupov, A. Agranovskaya, and N. Kranik, Sov. Phys. Solid State 2, 2651 (1961) and Fischer et al., J. Phys. Solid State Phys., 13, 1931 (1980). Thus, BiFeO3 offers the possibility of manipulating the magnetic state by an electric field at room temperature. See Ramesh et al., Nat. Mater., 6, 21 (2007). Recently, Zhao et al. showed evidence of coupling between the ferroelectric and magnetic order parameters in BiFeO3. See Zhao et al., Nat. Mater., 5, 823 (2006). The magnetoelectric coupling in BiFeO3 has also been suggested to enable the switching of a ferromagnetic material such as (La,Sr)MnO3 or Co coupled to the multiferroic through exchange interactions. See Chu et al., Mater. Today, 10 (10), 16 (2007). However, a prerequisite to exploiting such electrical control of magnetism is the reliable switching of ferroelectric domains in BiFeO3.